1. Field of the Invention
The present invention relates to an image forming apparatus comprising an automatic document feeder for automatically feeding an original onto an original table and for automatically ejecting the original from the original table.
2. Description of the Related Art
In a conventional image forming apparatus of this type, either when an automatic document feeder is used or when an original is manually set by an operator, an original is set on an original table with reference to one end of the original table. An exposure lamp for scanning the original set at the one end portion of the original table, with the light being moved between the one and the other end portions of the original table along the original table. Light projected from the exposure lamp toward the original table is slightly inclined from a direction perpendicular to the original table in a direction of the one end portion of the original table.
Recently, the applicant has developed an image forming apparatus in which, when an operator manually sets an original, he or she must set it at one end portion on an original table, and when an original is set on the original table by means of an automatic document feeder, it is set at the other end portion on the original table.
However, when an automatic document feeder is used in this image forming apparatus, the following problems arise. That is, since a projecting direction of light from an exposure lamp is inclined as described above, when the exposure lamp is moved to the other end portion of the original table, some light components from the exposure lamp are attenuated by the edge of the other end portion. These attenuated light components form a dark region on an original set at the other end portion on the original table as compared to a bright region irradiated with light which is not attenuated. Therefore, two dark and bright regions corresponding to the dark and bright regions are formed on a copied image, and an image in the dark region cannot be clearly reproduced.
A known automatic document feeder in the image forming apparatus comprises an original pickup means for picking up originals one by one from an original feed tray on which a plurality of originals are stacked, and a convey means for conveying an original picked up from the original feed tray toward the original table. The convey means is arranged in a cover for covering the original table, and has an endless conveyor belt having a large width and a belt drive mechanism for driving the endless conveyor belt. The convey means feeds an original picked up from the original feed tray by the original pickup means onto the original table to set it at a predetermined position on the original table, and ejects the original on the original table onto an original eject tray arranged at a side opposite to the original pickup means.
Recently, the applicant has developed an image forming apparatus comprising an automatic document feeder with which an original picked up from an original feed tray by an original pickup means is set at a predetermined position on an original table by a convey means, and after an image copying operation for the original is completed, the original on the original table is fed in a direction opposite to the feed direction from the original feed tray onto the original table to be ejected onto an original eject tray mounted on an original table cover.
In this image forming apparatus, a plurality of gate means are arranged between the original pickup means and the convey means of the automatic document feeder. These gate means direct an original, picked up from the original feed tray by the original pickup means, toward the original table, and direct the original fed from the original table by the convey means toward the original eject tray. However, the arrangements of these gate means are complicated, and their manufacturing cost is high.
In the known automatic document feeder described above, the next original cannot be fed onto the original table unless the original, set at the predetermined position on the original table, is completely ejected from the original table Therefore, it takes a long time to exchange originals on the original table. Consequently, when a large number of originals are copied, the total time required for exchanging the originals is considerable.